The invention relates to flexible shaft couplings, but more particularly, the invention relates to centering devices which define a positive center of rotation for angular misalignment between two shafts interconnected with a flexible coupling.
Centering devices are used in flexible couplings to define a positive center of rotation for two angularly misaligned shafts or rotating components, and to minimize run-out and balance problems. A centering device is usually required where flexing elements of a coupling do not per se define a kinematic center as for example, in a spring-type or double cardan coupling. A typical centering device includes a ball retained in a socket which permits unrestrained angular movements within the limits defined by a cone. Another type of centering device includes a ball retained in a socket with a pin extending axially through an aperture in the ball. Ball, socket, or pin combinations are generally used for mechanical element couplings such as the double cardan type, but they also may be used with flexible element couplings that are tubularly shaped. Examples of tubularly shaped flexible element couplings appear in U.S. Pat. Nos. 3,347,061; 3,621,674; 3,628,352; and 3,855,817.
The tubularly shaped flexible elements present a problem not found with mechanical type couplings. In mechanical type couplings, the balls, socket, or pin do not have to be physically retained together if failure occurs. Should the coupling fail, shafts coupled therewith are mechanically retained to each other by other metal components of the flexible coupling such as by a "yoke" and "cross."
Tubularly shaped elements present another problem, especially where spring type members are used. The failure of the tubularly shaped element results in a mechanical disengagement of two shafts because there is nothing to hold the shafts together after the tubularly shaped element fails. Another problem associated with centering devices for tubularly shaped elements is that they do not facilitate easy assembly or adjustment means that accommodate assembly tolerances. Assembly to a controlled tolerance is particularly difficult with tubular couplings as disclosed in the U.S. Pat. No. 3,855,817. This invention is primarily directed to centering devices for use with tubularly shaped flexible couplings.